Two parallel trenchless crossings, passing under the T7 tramway, were completed last week just north of Paris’ Orly airport. Though they weren’t the longest, they weren’t the simplest either !
With a busy dual carriageway, one of France’s biggest shopping centres and a multitude of underground networks nearby, finding a drill path for not one, but two, crossings meant going under the water table. From engineering to execution, project teams faced significant challenges:
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- Avoiding the mass of existing underground networks
- Constructing parallel drill paths with limited surrounding space at the exit
- Managing the water flow and welding under the water table
- The high volume of road traffic and pedestrians
OPTIMUM engineers designed all the retaining structures and crossings for project owner RTE, minimising the risk of ground settlements and vibrations under the tracks above. They then supervised all the construction works onsite: two parallel 45-metre-long, DN 600, down-the-hole (DTH) hammer drills, a slide-rail entry shaft and a timber exit shaft. Two stepped wooden pits were also designed to facilitate insertion of the ducts / cables, given the congested urban environ.
With these crossings now complete, RTE can continue the construction of its 225kV underground link to increase client capacity and reinforce network security in the area.
